They are notorious for "falling off" SmartThings and Hubitat networks and likely anything besides their own hub. If you haven't read this thread, it's pretty much a must-read for using them. While written for Hubitat, the takeaway message is equally applicable to ST: Xiaomi & Aqara Devices - Pairing & Keeping them connected. That message is basically "only use Xiaomi-friendly repeaters," of which very few are known (though pairing close to the hub is likely a good way to prevent them from trying something else, it's still no guarantee, and if you're only using ST for this and don't have Zigbee repeaters, then it's even more mysterious...).
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